class_docstr: Base class for feeds.
  
  :param maxLen: The maximum number of values that each :class:`pyalgotrade.dataseries.DataSeries` will hold.
      Once a bounded length is full, when new items are added, a corresponding number of items are discarded
      from the opposite end.
  :type maxLen: int.
  
  .. note::
      This is a base class and should not be used directly.
class_docstr_tok: ["Base","class","for","feeds",".",":","param","maxLen",":","The","maximum","number","of","values","that","each",":","class",":","`","pyalgotrade.dataseries.DataSeries","`","will","hold",".","Once","a","bounded","length","is","full",",","when","new","items","are","added",",","a","corresponding","number","of","items","are","discarded","from","the","opposite","end",".",":","type","maxLen",":","int",".","..","note",":",":","This","is","a","base","class","and","should","not","be","used","directly","."]
docstr: Returns True if a :class:`pyalgotrade.dataseries.DataSeries` for the given key is available.
docstr_tok: ["Returns","True","if","a",":","class",":","`","pyalgotrade.dataseries.DataSeries","`","for","the","given","key","is","available","."]
code: def __contains__(self, key):
      """Returns True if a :class:`pyalgotrade.dataseries.DataSeries` for the given key is available."""
      return key in self.__ds
  
file_path: pyalgotrade/pyalgotrade/feed/__init__.py
imports: import abc
  from pyalgotrade import observer
  from pyalgotrade import dataseries
label_desc: Use image node_id 12 for calling the BaseFeed obj's underlying member method code with example usage: obj.__contains__(key) and returns: unknown